A variety of methods have been hitherto known to propagate potatoes by tissue culture.
There is known a method for obtaining potato tubers which comprises culturing a tissue of potato, removing roots and leaves from the obtained plant and subjecting the stem to liquid culture [CIP Circular, vol. 13No. 4, December, pages 1 to 5 (1985); Plant Cell, Tissue and Organ Culture, 7:3 to 10 (1986)].
According to this method, the culture is performed by charging medium in a flask very thinly; thus, potato tubers are formed in the aerial phase and their numbers are not so large.
There is also known a method for propagation which comprises culturing a potato tuber and culturing the obtained plant, while repeatedly dividing it [American Potato Journal, 55: 691-701 (1978)]. However, even in the most efficient method, only 140 plants are obtained in 16 weeks. There is known a method for efficient propagation of small-sized potato tubers (Soshiki Baiyo (Tissue Culture), 11 (9), 391-395, 1985). The potato tubers formed by this method are of an adzuki size (about 0.1 g) to of an peanut size (about 0.7 g) in approximately 100 days after culture. In addition, single medium and culture conditions are utilized for the culture throughout the whole period. Further the culture is performed in a small-sized container and it is difficult to enlarge a culture scale.
It has been desired to develop a method of efficiently producing potato tubers having a weight of 1 g or more in mass culture.
In the case of Colocasia esculenta, Dioscorea japonica and Pinellia ternata, propagation of plants by tissue culture have succeeded, but a technique to efficiently propagate corm of a Colocasia esculenta, Pinellia ternata, and Dioscorea japonica tuberous root has not been developed [Yasai Shikenjo Hokoku A (Report A of the Vegetable Laboratories), 9: 1-46 (1981), Soshiki Baiyo (Tissue Culture), 11: 372-376 (1985)].
It has been desired to develop a method for efficient propagation of corm of Colocasia esculenta, Amorphophallus konjac, Pinellia ternata, a Scopolia japonica rhizome and a Dioscorea japonica tuberous root by tissue culture in large quantities.